The present invention relates generally to switching systems, and more specifically to an asynchronous transfer mode (ATM) switching system which is suitable for application to integrated services digital networks (ISDNs).
With the ATM switching systems currently under development, self-routing networks are contemplated for routing a "cell" by reading a successive bit of the logical channel number contained in the cell header as it finds its way through several stages of elemental switches to a desired output terminal of the network. Because of the self-routing nature of the network, there is a likelihood that several cells simultaneously want to access the same output terminal and congestion results at that terminal. To solve the congestion problem, cell buffers are connected to the output terminals of the self-routing network to store a cell in a waiting line when the associated transmission line is found busy and forward it immediately when the line becomes available. The storage capacity of each buffer is so determined that it can handle cells with a probability that a buffer overflow occurs for every 10.sup.9 to 10.sup.10 cells.
In order to handle calls with a speed as low as 64 kbps to calls as high as 150 Mbps using buffers of finite capacity while keeping the probability of buffer overflow at a considerably low value, it would be necessary to employ call restriction procedures to limit the number of calls to be accepted. However, this procedure would result in low utilization efficiency of transmission lines.